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July 14, 2011 -- People who say they vigilantly apply sunscreen are more likely to experience painful, damaging sunburns, a new study shows.

The study, the first to look at how people in the U.S. shield themselves from the sun and how well those different strategies work, analyzed information on more than 3,000 white adults that was collected through the National Health and Nutrition Examination Survey.

Sunscreen was the most commonly used kind of protection, grabbing the top spot with 30% of people saying they regularly apply it when they’re outside for longer than an hour.

The next most common skin-saving strategies were seeking shade (25% said they frequently stayed under cover when the sun was blazing), wearing a hat (16%), and donning long sleeves (6%).

People who said they frequently used sunscreen, however, had 23% greater risk of multiple sunburns in the past year compared to people who said they seldom used the stuff.

Those who frequently sought shade and pulled on long sleeves, however, had about a 30% lower sunburn risk compared to people who rarely used those measures.

Those risks remained even after researchers corrected for factors known to influence burn risk, including the skin’s sensitivity to the sun, alcohol use, season, physical activity, age, gender, education, and income.

Avoiding Sun Important, Too

“I really like this study,” says Ronald P. Rapini, MD, professor and chairman of the department of dermatology at the University of Texas M.D. Anderson Cancer Center in Houston. “I’ve always felt the same way, and I tell my patients the same thing.”

“Just last week, one of my melanoma patients came in with a sunburn all over their back, and I said, ‘What happened?’ and they said, ‘Well, I had sunscreen.’ But they missed an area on their back, which is what always happens. They think that they can stay out in the sun because they’re using sunscreen, and the truth is it doesn’t really cover stuff that well,” says Rapini, who was not involved in the research.

“Myself, personally, I’m a dermatologist, and I don’t even wear sunscreen all that much. I stay in the shade,” he says. “I try to stay out of the sun.”

More Sunscreen, More Sunburns

“I was quite surprised to find the associations that we’ve found with the different types of sun protection,” says study researcher Eleni Linos, MD, DrPH, MPH, a dermatologist at Stanford University.

“What we saw was that wearing long-sleeved clothing, wearing a hat, and staying in the shade were associated with fewer sunburns,” she says. “However, wearing sunscreen was actually associated with more sunburns.”

Linos is quick to point out that her results don’t mean that sunscreen doesn’t work or shouldn’t be used.

The study was designed to look at patterns, not to prove cause and effect.

It’s possible that people with the fairest, most easily burned skin are also simply the group most likely to use sunscreen.

But if that were the case, Linos says, she would have expected to see the same phenomenon across all the different groups. That is, frequent shade seekers and long-sleeve wearers would also report having more burns compared to those who rarely reported those tactics.

The more likely explanation, she thinks, is user error -- people simply aren’t applying as much sunscreen as often as they should.

Numerous studies have shown that most people, even after they’re carefully schooled in proper sunscreen application, still don’t get enough on.

One of the latest, from researchers in Brazil, asked study participants to cover both forearms with sunscreen, and 30 minutes later, to reapply the sunscreen to just one arm.

Researchers used tape strips to measure how thickly the lotion went on.

Sunscreen is tested to work at its SPF when it’s applied to a depth of at least 2 milligrams per square centimeter on the skin.

After the first application, study participants got only a quarter of that amount on. For the arm that got the second application, the depth of the sunscreen eventually reached half of what it should have been, suggesting that even people who remember to reapply aren’t being fully protected.

Shade, Hat, Sleeves

Another problem is that many people rely on sunscreen as their sole form of protection, when really, shade and protective clothing need to be part of a multi-pronged approach to avoiding sunburns, which increase the risk of skin cancer.

“There’s still a lot of work that we as physicians, especially dermatologists, need to do to educate individuals about proper photoprotection,” says Henry W. Lim, MD, chair of the department of dermatology at Henry Ford Health System in Detroit.

He says this study is consistent with previous research.

“It’s known that people use sunscreen, but they don’t use it at the appropriate amount and because of that, they have a false sense of a security,” says Lim, who was not involved in the research.

That false sense of security can lead people to stay in the sun longer than they safely should, leading to an increased risk of sunburns and greater UV exposure, which can cause skin cancer.

Sunscreen Prevents Cancer

Sunscreen use has been shown to reduce some kinds of skin cancers, however, and earlier this year, a prospective study, the first of its kind, found that regular sunscreen use in a group of 1,621 Australian adults cut their risk of melanoma by 50%.

Importantly, however, the study participants in that trial carefully and repeatedly applied sunscreen while also seeking shade and wearing protective clothing.

“The best data that’s out there shows the combination of seeking shade, wearing protective clothing and wearing sunscreen, those three things together clearly lower your risk,” says Darrell S. Rigel, MD, a clinical professor of dermatology at New York University.

Rigel says there is an important caveat about this study which should reassure people about their sunscreen.

The latest data used in the study is now about five years old, and he says sunscreens have improved in a couple of key ways since then.

“How long it lasts, 'substantivity' it’s called, has markedly improved, really with new formulations,” he says, and many of the newer formulations offer better broad-spectrum protections against both UVB, the burning rays, and UVA, the cancer-causing rays.

New FDA rules for sunscreens, which will go into effect next year, should make it easier to pick a good product.

That’s important, Rigel points out, because it’s not always possible to stay in the shade or wear longs sleeves.

In those cases, it’s more important than ever to put sunscreen on correctly.

Experts say the rule of thumb is a golf ball-sized blob for every exposed body part, applied at least 30 minutes before going outside, since sunscreen takes that long to absorb into the skin.

That much sunscreen should be reapplied every two hours, and even more frequently, every 60 to 90 minutes, when swimming, sweating, or using a spray product, since those don’t last as long.